25.06.2014: Researchers at the GFZ German Research Centre for Geosciences have found a new method for studying the structure of the solar corona using radio interferometry. The solar corona is the outer part of the Sun's atmosphere and consists of fully-ionized plasma with temperatures above one million degree Celsius. Its structure is primarily characterized by the coronal electron density. The GFZ researchers report in the current issue of “Nature Communications” that they have developed their electron density models based on data from very long baseline interferometry (VLBI).

VLBI is an important technique for geodesy and astrometry, using a global network of radio telescopes to record signals from extragalactic radio sources. “For the first time we were able to create coronal electron density models using VLBI data”, says Benedikt Soja from GFZ. “A comparison of our results with previous models showed very good agreement.” And not only that: the scientists could find out that regional variations in electron density are detectable by VLBI and that on average the electron density in active regions is about three times that of low-density regions.

Understanding the characteristics and mechanics of the solar corona is not only important for solar research: By monitoring the state and structure of the corona, space weather predictions are possible, crucial for instance for satellite operations, space flights activities or telecommunications. Space weather has also an important impact on the Earth's ionosphere and the geomagnetic field. Compared to the hithereto existing methods, the advantage of the new VLBI approach is its potential ability of monitoring the solar corona in a homogenous and continuous way. The results of the GFZ researchers imply that VLBI will be of great benefit to future investigations of the solar corona.

Soja, B., Heinkelmann, R., Schuh, H.: “Probing the solar corona with very long baseline interferometry”; Nat. Commun. 5:4166 doi: 10.1038/ncomms5166 (2014).